This invention relates to camming elements for fasteners, and particularly, though not exclusively, to camming elements for fasteners for use in the furniture industry.
A known fastener for holding two members together is illustrated in FIGS. 1 to 3. The fastener includes a camming element 1′ and a dowel 2′. The dowel 2′ is fixably attached to a first one of the members 3′, by a screw thread, for example. The other, second, member 4′ has a circular hole 5′ in which the camming element 1′ can rotate, and a bore 6′ perpendicular to and intersecting the circular hole 5′, whereby the dowel 2′ can be inserted into the bore 6′ so that a head 7′ of the dowel 2′ protrudes into the circular hole 5′.
Rotation of the camming element 1′ causes first and second camming surfaces 8′, 9′ of the camming element to engage with the head 7′ of the dowel 2′, and further rotation of the camming element 1′ pulls the head 7′ of the dowel 2′ further into the circular hole 5′. This, combined with the attachment of the dowel 2′ to the first member 3′, causes the first member 3′ to be pulled toward and fastened to the second member 4′.
Rotation of the camming element 1′ is effected by applying torque to a torque connecter 10′, an example of which is a cross-head screw slot that allows the rotation and camming action of the camming element 1′ to be driven using a standard screwdriver 11′.
Conceptually, the camming element 1′ can be thought of as roughly cylindrical, being formed of three coaxially arranged spaced discs. The first of these discs has an outer surface along part of the circumference of the cylinder for contacting the circular hole 5′ in the second member 4′. The disc is cut away to produce the first camming surface 8′, which is to contact the head of the dowel 2′. The second disc is shaped similarly to the first, and is positioned such that there is a slot between the first and second discs. The third disc is positioned so that second disc is between the first and third discs. The third disc is not cut away, and has the torque connecter 10′ at its centre. The third disc has the function of providing a covering for the circular hole 5′. It should be noted that the phrase “cut away” is used to describe the shape of the camming element 1′, and does not imply a particular method of manufacture.
In the field of camming fasteners, reduction of weight and materials is considered desirable. This is particularly true when the fasteners are made from expensive materials, such as zinc. In this case, a reduction in weight, or equivalently the amount of raw material required, can lead to a considerable reduction in cost. Weight can be reduced by coring. Coring is well known in the art and is a process of removing unnecessary material from a component. As is well known, the “removal” of material can take place at the design stage, and does not necessarily require physical removal of material. In relation to camming fasteners, it is known to perform coring from the first and second discs by removal of material from the faces between the first and second discs. FIGS. 1 and 3 show an example of a conventional camming element with first and second discs having cored inside faces 13′ and 14′.
In the known camming fasteners, the camming element can tilt within the circular hole, leading to the first 3′ and second 4′ members becoming loose with respect to each other. This is undesirable, and can lead to a loose joint and failure of the fastener. For example, when the fasteners are used in the furniture industry, tilting of the camming element 1′ can lead to wobbly furniture.
In known designs, it is possible for excessive torque to be applied via the torque connector 10′, leading to damage or destruction of the camming element 1′. In particular, the third disc, via which torque is applied, can shear off the second disc. In commercially available fasteners, it is possible for the camming element 1′ to be damaged or destroyed by torques that can typically be applied manually with a standard screwdriver.